92 THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



maxillary and mandibular processes, second and third branchial arches, arid 

 cervical sinus (cf. Fig. 93). The brain is differentiated into the five regions, 

 telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon. 

 The spinal cord is cylindrical and gradually tapers off to the tail. The anlages- 

 of the cerebral and spinal ganglia and the main nerve trunks are shown. The 

 oculomotor nerve begins to appear from the ventral wall of the mesencephalon. 



J ii^ithtr ^luig. u. JO 

 G<!n<j,. nodusjim n. I 

 X . ii! ccssoran 



Sup. gang. n. g Otocyst 



Acoustic ganglion 



Gdng. Fi'uricp 



Gang. I'crv 

 N. hypoglo.^Mis 

 Cervical sinus 



Atrium 



Ventral lobe liver-j 

 Dorsal lobe liver- 

 Thoracic gang. I 



Mesonephros 

 Small intestine 



Gciiiciiliilc i'dHi;. H. 7 



.Semilunar i;iiiig. n. j 



}[i t' iicepkalon 



Mi:si_iicephalon 

 i\'. oc ulomotorius 



Diencephalon 

 Petrosal gang. 



It. u 



Lcn^ opening 

 Olfactory pit 

 Tcicncepkalon. 

 T(tlk sac 

 AUautois 



Ventricle 

 AHanioic stalk 



Hijld-gltt 



Fig. 95. — Dissection of a 5.S mm. pig embryo, showing the nervous system and viscera from the right 



side. X 18. 



Ventro-lateral to the metencephalon and myelencephalon occur in order the 

 semilunar ganglion and three branches of the trigeminal nerve; the geniculate 

 ganglion and nerve trunk of the n. facialis; the ganglionic anlage of tlie n. acusticus 

 and the otocyst. It will be observed that the nerve trunks are arranged with 

 reference to the branchial arches and clefts. Caudal to the otocyst a continuous 

 chain of cells extends lateral to the neural tube into the tail region. Cellular 



